DESCRIPTION The objective of this research is to determine how expression of c-type cytochromes is regulated. These hemoproteins are vital for energy- producing electron transport chains of eukaryotes and many prokaryotes, and defects in their production have been associated with mammalian mitochondrial myopathies. To understand how production of these proteins is controlled, this fellowship will focus on cytochrome c2 of the facultative phototroph Rhodobacter sphaeroides. In this organism, cytochrome c2 is a multi-functional electron carrier that is utilized in different energy-producing transport chains depending upon the metabolic state of the bacterium. The proposed experiments will address how expression of the cytochrome c2 gene is regulated under anaerobic conditions, in response to the alternative electron acceptor dimethyl sulfoxide during anaerobic respiration, and in transitions between various aerobic and anaerobic lifestyles. The results of these studies will provide a detailed picture of the new regulatory hierarchies that control expression of multi-functional electron carriers such as cytochrome c2.